The technical field of the invention pertains generally to lasers and more particularly to preionized excimer laser devices and the like.
Excimer or "excited dimer" lasers are pulsed gas lasers which typically employ mixtures of halogens and rare gases, together with buffer gases and other additives to create an active medium. When pumped to an electronically excited state, the rare gas and halogen ions form dimer molecules. These molecules emit high intensity, short wavelength radiation when they relax and return to the dissociated ground state.
One method of exciting the active medium of an excimer laser is by an avalanche electric discharge. In an electric avalanche discharge laser, the medium is excited by a flow of electrons from a high voltage electrode across the medium to ground. Electric avalanche discharge lasers offer substantial promise for research and medical applications, in particular, because they can yield convenient energy outputs with very fast pulse repetition rates.
Most excimer lasers that emplgy avalanche electric discharges also "preionize" the medium. Preionization permits the deposition of additional energy per pulse and, hence, higher output power densities. Conventional techniques for preionization employ a spark array to generate ultraviolet radiation. Such preionization circuits typically terminate operation as soon as the avalanche discharge commences.
A number of factors, however, limit the efficiencies, pulse lengths and pulse rates of presently available electric discharge excimer lasers. Typically, the avalanche discharge lasts for about 20 to 30 nanoseconds before heating and instabilities result in arcs that terminate the laser output.
There exists a need for better lasers, particularly excimer lasers and the like. There exists a need for better ionization schemes that would sustain pumping by avalanche discharge techniques and, thereby increase beam uniformity at high repetition rates.